The energy minister, Volodymyr Demchyshyn, said that there was “no threat” from the accident and that the malfunction had taken place in the section of the plant responsible for distributing power, not among the reactors in the section for generating power.

Zaporizhia, the largest nuclear power plant in Europe, is in southeast Ukraine on the banks of the Dnieper River. It is in territory controlled by the Ukrainian government, and it is about 150 miles west of Donetsk, a city held by the separatist rebels.

A press officer at the Energy Ministry said by telephone that the damage was “minor” and “insignificant,” adding that repairs should be finished by Dec. 5.

A statement posted by the press office of the power plant said that the reactor’s third generating block had been shut down for repairs on Nov. 28. The reason for the repairs was not given, although the statement said that there were no health threats and no increase in radiation levels.